From the aforementioned patents and the art mentioned therein it is known to provide for the transport and storage of radioactive wastes, containers or vessels of radiation-shielding material and which may be provided with channels or compartments to contain radiation-blocking and radiant-energy-attenuating material and with ribs or the like to promote heat exchange with ambient air.
Radioactive material can be placed in such containers and sealed by cover arrangements including a shielding cover which can have a plug configuration, i.e. which is comparatively massive so that it functions as a radiation-absorbing wall, the seal between this cover and the vessel being labyrinth or multiple seal having sealing rings between surfaces which are stepped or at angles to one another to minimize the probability that a radio nucleide particle can pass between the cover and the vessel and thereby escape.
The vessel can have a mouth formed with a recessed seat receiving the plug-type inner cover which can have a frustoconical portion and a cylindrical portion fitting into correspondingly shaped parts of the seat and sealed relative to the latter with elastomeric seals, generally O-rings.
Above this inner cover, an outer cover was mounted on the vessel as a protective member. Seals could be provided between this outer cover and the vessel as well and an important feature in the packaging of the radioactive material was the including of a control gas whose composition could be monitored or "sniffed" to verify the security of the seals.
Between the outer cover and the inner cover, therefore, a control space was provided and this space was monitored to detect the stability of the seal.
Both the vessel and the plug-type cover can be composed of cast iron, especially spherolytic cast iron or cast steel and the plug-type cover can be sealed to the vessel with an inner seal which can be of the single-stage or multiple-stage type.
The safety cover, which is disposed above the shielding cover and defines a control-gas compartment therewith, is formed with the outer seal and can be overlain by a further protective cover, if desired.
While packaging of the afordescribed type has proved to be effective for the transportation and long term storage of radioactive waste, monitoring of the integrity of the package, i.e. the integrity of the seals, has required monitoring of the presence in the control-gas compartment of radioactive species whose presence can signal a defect in the inner seal.
Repair of the system, by removal of the outer cover, removal of the safety cover, and resealing the plug-type cover may result in release of any radioactive components in the control space between the safety cover and the plug-type cover.
Furthermore, the detection of a failure is effected by analytical means requiring sniffing with sensitive species-discriminating detectors which may not always be reliable.
Earlier techniques did not adequately signal a failure of the outer seal, i.e. the seal between the atmosphere and the control space.